This study aims to estimate the state of fish communities in the basin of River Casin in 1998-2008 based on some indices of biodiversity (Alpha, Berger-Parker, Simpson). There were established some physic-chemical factors of the water and there were made some correlations between biodiversity indicators and some abiotic factors. It was observed that the value of biodiversity indices varies in time and depends on the sampling sites, suggesting a clear influence of the anthropic factors on the biodiversity within fish communities.